1. Field of the Invention
The present invention relates to a conveying apparatus that conveys sheets.
2. Description of the Related Art
Some of recording apparatuses that perform printing on a paper sheet have a conveying apparatus that substantially horizontally loads and holds paper sheets in a lower portion of a recording apparatus main body and carries out so-called U-turn sheet feeding, i.e., conveying a paper sheet along a substantially U-shaped conveying path (which may be referred to as a U-turn path in some cases) before performing printing on the paper sheet. In such a conveying apparatus is provided a sheet feeding roller pair arranged upstream of the conveying path or a conveying roller path arranged downstream of the conveying path. Further, to cope with conveyance of small-sized paper sheets, some conveying apparatuses have an intermediate roller pair arranged at a halfway point of the conveying path besides these roller pairs. These roller pairs rotate while nipping a paper sheet and carries the paper sheet.
In the conveying apparatus having such a configuration, an operation for correcting an inclination (a skew) of a paper sheet that occurs in a paper sheet conveying process may be performed. Specifically, during conveyance of a paper sheet using the intermediate roller pair, an end of the paper sheet that is being conveyed is arranged to abut on the conveying roller pair that is stopped or rotated in a reverse direction, and the end of the paper sheet is aligned with a nip line of the conveying roller pair, thereby correcting the skew of the paper sheet. This abutting operation enables correcting the inclination of the paper sheet at the end portion of the paper sheet. However, the intermediate roller pair that conveys the paper sheet keeps nipping in a state that a central portion or a rear portion of the paper sheet is inclined, whereby the paper sheet is twisted between the end of the paper sheet and the central portion or the rear portion of the paper sheet. When the skew of the end portion of the paper sheet is corrected, the conveying roller pair that is stopped or rotated in the reverse direction is rotated in a forward direction, the end of the paper sheet is nipped, and the paper sheet is conveyed, but this twist of the paper sheet can be a factor that again inclines the paper sheet to cause the skew of the paper sheet.
As a method for coping with this problem, as disclosed in U.S. Pat. No. 7,533,878, there is a method of using an intermediate roller pair having rollers (swing arm type rollers) disposed to an arm that swings around a fixed shaft. The swing arm type roller increases a nip pressure with an increase in conveying resistance from the paper sheet received by the rollers or reduces the nip pressure or releases the nip. Here, the nip pressure means a pressure that is applied to the nipped paper sheet from the roller pair. Further, when driving of the rollers is stopped immediately after correcting the inclination of the paper sheet so that the conveying resistance from the paper sheet is not received, the nip of the paper sheet can be released, and the torsion caused at the time of correcting the inclination of the paper sheet can be eliminated.
In a conveying apparatus for use in a recording apparatus typified by an ink jet recording apparatus in recent years, miniaturization and realization of a low cost are demanded. Therefore, it is desirable to drive the conveying roller pair and the intermediate roller pair by a single motor without providing different motors for these roller pairs. When both the roller pairs are driven by the single motor, it is difficult to stop driving the intermediate roller pair alone like U.S. Pat. No. 7,533,878.
Further, in the swing arm type roller, when a paper sheet nipped by a pair of rollers is pulled at a higher velocity than a circumferential velocity of the swing arm type roller, conveying resistance of the paper sheet is reduced or eliminated, and hence the nip of the paper sheet is released. In this case, when the circumferential velocity of the conveying roller pair on the downstream in the conveying direction is increased beyond the circumferential velocity of the intermediate roller pair on the upstream in the conveying direction, distortion caused at the time of correcting the skew of the paper sheet can be annihilated.
Some of recording apparatuses perform printing on both sides of a paper sheet. Such a recording apparatus has a conveying apparatus that can pass a paper sheet to another conveying path (which may be referred to as a reversing path in some cases) and again convey the paper sheet to a printing portion with the paper sheet being reversed after arranging a front side of the paper sheet to face the printing portion through the conveying path (a U-turn path) and effecting printing.
In the reversing path, the paper sheet can be conveyed from the conveying roller pair to the intermediate roller pair through a path different from the U-turn path and, in this case, the paper that has reached the intermediate roller pair is again conveyed to the conveying roller pair like the U-turn path. In this case, the conveying roller pair is placed on the downstream of the intermediate roller pair (see also FIG. 1A) in the U-turn path, but the conveying roller pair is placed on the upstream of the intermediate roller pair in the reversing path (see also FIG. 1B). Therefore, when the paper sheet is conveyed through one of the paths, a conveying velocity of the roller pair on the downstream is lower than a conveying velocity of the conveying roller pair on the upstream. As a result, in the roller pairs, the paper sheet adheres to the outer periphery of each path and then buckles, which results in a problem that a skew or a jam occurs.